<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>变量演示</title>
</head>
<body>
<script type="text/javascript">

    var a=100;
    // alert(typeof(a));//number
    var b="abc";
    // alert(typeof (b));//string
    var c;
    // alert(c);//undefine
    var n1=12;
    var n2="abc";
    alert(a*b);//NaN


</script>
</body>
</html>